Telephone-exchange system



June 19, 19253. 1,459,185

' L. PQLENKOWSKY TELEPHONE EXCHANGE SYSTEM Filed AprilBO, 1920 3 Sheets-Sheet 1 w, 223. mama L. PQLINKOWSKY TELEPHONE EXCHANGE SYSTEM Filed April 30, 1920 3 Sheets-Sheet 5 3+8 LUNG y M A l atented'dune 19, 1923.

iat t rarest" LIPA POLINKOWSKY, OF ANTWNERP, BELGIUM, ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N; Y., A CORPORATION OF NEW .YORK.

TELEPHONE-EXCHANGE svsrnirp Application filcd April 30. 1920. Serial No. 377,980.

T 0 all whom it may concern:

lie it known that I, Lira PoLiNxoWsKY, a citizen of Russia, residing at Antwerp, Belgium have invented certain new and useful Improvements in Telephone-Exchange Systems, or which the following is a full, clear, concise, and exact description.

This invention relates to telephone systerns and particularly to systems in which machine switching apparatus is used for establishing connections between subscribers lines.

g The object of this invention is the provision of means, in a system where the selec tive switches are operated under the control of register controlling devices, whereby a single registration is effective to control aplurality of selective movements of the switches in the extension of a connection.

A feature of the invention relates to the provision of means operable in accordance with the selective movement of a switch to produce a registration corresponding to such movement, and which means is thereupon effective to control the selective movement of a succeeding switch in the extension of a connection.

Another feature of the invention relates to the provision of means, operative on the release of the switches, for simultaneously rendering selectable both ends of the trunk lines extending between such switches.

Other features of the invention will be come more apparent'from' a consideration of the following description and appended claims.

In the drawings, Figs. 1, 2 and 3, taken in order illustrate so much of a telephone system as is necessary to an understanding of the invention. 7

Fig. 1 illustrates diagrammatically a group selector switch and a register controlling mechanism. Fig. 2 shows a selective switch in the central oiiice having access to trunk lines outgoing to a distant private branch exchange. Fig. 3 shows the incom ing end of the central office trunks terininating in connecting switches in the private branch exchange. v

In the system disclosed there is provided a central OfilCQ equipped with group selector switches such as the one illustrated diagrammatically in Fig. 1, and a register controlling mechanism for controlling the selective operation of these switches and also succeedmg switches in the establishment of connections There is also provided in the central otlice special selective switches, such as the one shown in Fig. 2, for exteiidingconnections to trunk lines leading to distantprivatfe branch exchanges. "When a subscriber in the central office desires to obtain a connection with another subscriber local to the same office, he causes the positioning'of the registers in accordance with the number of the desired line. Theseregisters are then etitective to control the selective operations of I the switches in the central office to complete the establishment of theconnection. When however, a connection is desired with a subscribers line belonging to a distant private branch exchange, the record set up on the controllingregisters causes the group selecting switches shown in Fig. 1 to select atrunk leading to one of the special switches in the central oflice. This switch is then operated under the control of the tens register to select a level of trunks outgoing to the desired private branch exchange. The movement of the special switch,-in the selection of the desired level of the trunks, determines the setting of a register associated, with such switch in accordance with the registration which control'sthe switch in its selec-tiono f the level 01": outgoing trunks. By this "means the tens registration, which determines the selection of the proper level of trunks out} going to the private branch exchange, is

reproduced on the register individual to the switch. The switch, after having chosen the proper level of trunks, operates automati-- cally to select an idle trunk in the level leading to the final connecting; switch in the private branch exchange. This final connecting switch is then operated under the control of the individual'register to select a level of subscribers lines. After having selected the proper level of lines,the 'final switch in the private branch exchange is then operated under the control of the units register of the register controlling inechanism in the central ottice to complete the connection to the called line.

controlling said switches may be of the type shown and described in the patent to P0- linkowsky No. 1,365,269, granted January In the followin detailed description of the operation of t e system it is assumed that a-subscriber whose line terminates in the central ofi'ice, desires to hold a conversation with a subscriber whose line belongs ing line by way of conductors 115 and 116 to an idle register controlling mechanism. The calling subscriber then operates his impulse transmitter to position the registers 130, 140 and 150, in accordance with the called line designation.

Since the call is one intended for a subscribers line in the distant private branch exchange, the brushes of the first group selector 109, 110 and 111 are operated under the control of register 130 to select the terminals 112, 113 and 1 14 of a trunk leading to the special switch in the central office. When the test brush 111 encounters the test terminal 114, a circuit is completed from battery, winding of relay 243, contact 240 (1) of sequence switch250, terminal 114, brush 111, contact 108 of sequence switch 100, right-hand high resistance winding of test relay 107 to ground, In parallel to this circuit a circuit is also completed from battery through resistance 242, contact 241, contact, 240 (1), to ground through the Y winding of relay 107. Relay 107 energizes and closes a low resistance path to ground through its left-hand low resistance winding and contact and armature. Relay 243 becomes energized and closes a locking circuit for itself over its left-hand armature and contact, independent of sequence switch contact 240. At the same time the brushes 1.09 and 110, by making engagement with terminals 112 and 113 respectively,close the fundamental circuit for controlling the brush tripping operation of the switch. This circuit may be traced from battery through the winding of relay 252, contact 244 (1 to 2), terminal 113, brush 110, contact 106, conductor 117, winding of stepping relay 126, armature and contact of relay 125, contact 122 of sequence switch 120, closed in position 10, conductor 118, contact 105, brush 109, terminal 112, contact 245 (1 to 2) to ground. Relay 252 becomes energized and closes a circuit from ground through its armature and front contact, contact 253 (1), winding of sequence switch 250 to battery and ground. Sequence switch 250 advances from position 1 into'position 2. In position 2 of sequence switch 250 a circuit is closed from battery through the winding of trip spindle power magnet 248, contact 253 (2 to 4), front contact and armature of relay 252 to ground. The power magnet 248 causes the rotation of the trip spindle to select the proper set of brushes.

VVhen the trip spindleis in its home position the interrupter brush 230 engages the comparatively deep notch 233. The notch 233 is so formed with respect to the remaining notches on the trip spindle element that brush 230 and contact spring 231 remain in engagement with each other at all times While the trip spindle is away from its normal position. The contact springs 231 and 232 are so disposed that they engage each other only during the time that the interrupter brush 230 is passing from one to another of the comparatively shallow notches in the trip spindle. element. These shallow notches, ot' which there are ten, correspond to the brush tripping positions of the switch. At the time the sequence switch 120 of the register controlling mechanism. reached position 10 prior to the closure of the fundamental circuit, a cuircuit was established from ground through contact 124, armature and contact of relay 126, left-hand winding of relay 127, armature and contact of relay 127, contact 123 (10), contact 1420f the tens register 140' through the winding of said register to battery and ground. A circuit was also completed from battery through the right-hand winding of relay 127 to ground at contact 124. Relay 127, being differential, is not operated when both its windings are energized simultaneously. The register 140, however, becomes energized and moves from the position to which it was adjusted by the calling subscribers transmitter to the next succeeding'position. When the master contact 141 of register 140 closes between positions, the left-hand winding of relay 127 is shunted out, permitting this relay to energize over its right-hand winding. When the fundamental circuit is closed, as above described, the stepping relay 126 becomes energized and opens the circuit of the right-hand winding of differential relay 127. Relay 127 thereupon deenergizes. As the brush tripping spindle leaves its normal position, a circuit is closed from battery through the winding of relay 252, contact 249 (2), conductor 234, contacts 232 and 231, and brush 230 to ground. This circuit maintains the energization of relay 252 and causes the shunting of stepping relay 126/ Relay 126, by releasing its armature, closes the abovetraced circuit for advancing the tens register 140 to its next succeeding position. This operation continues, the register 140 ad vancing one position for each deenergization of stepping relay 126 until said register reaches its normal position 0. In position 0 of register 140 a circuit is closed from battery through the winding of sequence switch 120, tact 143 (0), contact 123 (10), contact and armature and left-hand winding of relay 127, contactand armature of relay 126, contact 124 to ground. In parallel to this circuit, a circuit is also completed for the relay 125. Relay 125 operates to openthe fundamental circuit and sequence switch 120 passes from position 10 into position 12. As soon, after the fundamental circuit is opened at the register controlling mechanism, as contacts 231 and 232 are opened, relay 252 becomes deenergized. The retraction of the armature of relay 252 opens the circuit of power magnet 248 and also closes a circuit including contact 254 (2) for driving sequence switch 250 out of position 2 and .into position The tripping spindle has thus been rotated to a. position fortripping the set of brushes haying access to the desired level of trunks as determined by the setting of the tens register 140. The prin ciple by which the registers 130, 140 and150 of controlling mechanisms of this type are set in positions corresponding to the complements of the digits, is fully explained in the British patent issued to Western Electric Company, Limited, No. 146,517, accepted October 5, 1921.

When sequence switch 250 reaches position 3, a circuit is completed from battery through resistance 242, contact 241, contact 240 to 4), contact 269, brush 235, winding of relay 262 to ground. Relay 262 energizes in this circuit. While sequence switch 250 is passing through position 2% a circuit is closed from battery through the winding of relay 263, contact 245 (21-) to ground The contact 245 does'not open when passing out of position 21; until after contact 240 has closed in position 3 to permit the energization of relay 262, hence with relays 262 and 263 simultaneously energized, a locking circuit is completed as follows, for the latter of these relays: battery, through the winding of relay 263, front contact and right-hand armature of said relay, front contact and armature of relay 262, contact 254 (3 to 4), back contact and armature of relay 252 to ground. A circuit is now established from battery through the winding of brush carriage power magnet 261', front contact and left-hand armature of relay 263, contact 231, interrupter brush 230 to ground. Magnet .261 energizes and moves the brush carriage away from its normal contact 121 (10), con:

1 circuit from battery tact 253 (2 to 4),

through its right-hand winding.

contacts 232 and- 23,1 again open as the.

brush carriage, in moving away from its normal position, causes the tripping of the selected setofbrushes 282, 283 and 284.. Re lay 262, by deenergizing, opens the locking circuit of relay 263. armatures and Opensthe circuit of power magnet 261 causes the brush carriage to stop. Relay 263also completes a circuit from battery through the winding of relay 252, contact 244 (3 to left-hand armature of relay 26 3, contact 231, interrupter brush 230 to ground. lielay 252 becomes energized and completes a through the winding power magnet 248, confront contact and armature of relay 252 to ground. The trip spinof the trip spindle dle power magnet 248 energizes in this circuit and rotates forward to its normal position. It will be noted that since the trip spindle isprovided with ten tripping positions, it will passthrough a number of positions in its restoration to normal, which is the complement of the tens digit that serves to determine the selection of the proper set of brushes 282, 283, and 2840f the selective switch. For. example, if the tens digit is 6, the trip spindle'in rotating from this position to position zero covers four positions, the complement of 6. As will now be described, the trip spindle in passing through these complementary positions, serves to cause the setting of the individual register 290 in a position whereit is later effective to determine theIbrush-selecting operation of thefinal switch in the private branch exchange, in accordance with the tens digit. When the contacts 231 and 232 are first closed in the. restoration of the tripping spindle, a circuit is completed from battery through the winding of register 290, contact' 258 (3), left-hand winding and back contact andarmature of relay259, contact- 257 (3), conductor 234,,contacts 232 and 231, to ground. In parallel to this circuit, a circuit is also completed from' battery through the winding of coil 236, right-hand winding of relay 259, contact 266 (3), and thence to ground at contacts 231 and 230.

Relay 263- releases its 4), back contact and The relay. 259 being differential, does not operate when both of its windings are energized simultaneously. Register 290, however, becomes energized and advances from position 0 into position 1. Tn passing from position 0 to position 1, the master contact 291 closes and short-circuits the left-hand winding of relay 259. Relay 259 thereupon operates by means of current flowing brush 230 drops into thenentshallow notch,

When I cuit for register. posit on linto position 2. This operation a circuit for the right-hand Winding of relay 259 is opened to permit the release of continues until the trip spindle reaches its normal position at which time the interrupterbrush 230 engages the comparatively deep notch 283. This causes the separation of contact 231 and brush 230, ant the con sequent opening of the circuit of relay 252. Relay 252, by releasing its armature opens the circuit of trip spindle power magnet 248. p r

Relay 252 by deenerg'izing also completes a circuit from battery .tirough the Winding of brush carriage p'oWer magnet 261, back contact and armature of relay 262, contact 25% to 4), baclrcontact and armature of relay 252 to ground; Power magnet 261 energizes and causes the rotation of brushes 282, 283 and 284, over the selected level of trunks in search of an idle one thereof. The engagement of test brush 284 with test terminal 288 of an idle trunk, which is identified by the presence of a full battery I potential, ;closes a circuit from battery through the Winding of cut-oil "relay 287 terminal288 brush 28 1, contact 277 (3), left-hand hlgliTQSlStZlllCG Winding of test relay 264, to ground. Relay 264 becomes energized and completes a substitute low resistance circuit through its right-hand inding, contact and" armature and the winding; of. relay 262 to ground. 'This loW resistance path serves to reduce the potential oirthe multiples or terminal 288 to render the selected trunk bus to other switches. Relay 262 energizes and opens the circuit of the power magnet 261 to stop the brush, carriage. also completes a c rcuit from battery through the winding;

of sequence switch 250, back contact and right-hand armature of relay 263, front contact and armature of relay 262, contact,

25 i to l), back contact and armature of relay 252 to-ground. Sequence switch 250 passes through position land into position 5.

A Since itinay be desirable to use the trunk lines interconnecting the central oiiice and the privatebranch exchange, as two-t ay trunks, it is necessar t render the distant end of the trunlrline busy as soon as pos ible. To accomplish this the sequence switch 250 in position 5, completes circuit from the source of alternating current 287, contact 268 (5) brush 283, terminal286, conduct or 301 right-hand armature and back contact of relay 872, left-hand SVlHCllIlfZ of relay 373, 1 condenser 303, resistance 375, back contact and left-hand armature of relay 372, conductor 802, terminal 285, brush 282, contact 267 (5), Winding of relay 260,

to batte y and ground. Relay 260 is maru'inal and does .n 5 and "ate atracrsr are ature and closes locking;- cm

for itself "from battery through re- 'li'id,

condenser 303. Belay 373 contacta a. contact a armature-of rel ..y and. ltelay 5755 establishes acirnd i -;;'h arn'iature and f) to ground. Relay .1

'CllClljt from b of sequence '1 L 1 trout contact one comes energized completes a circuit from battery through the Winding of" sequerce switch 250, contact 258 (5 from contact and armature of relay 260 to ground. Sequence switch 250 advances from position 5 into position 6. In position 6 of sequence switch 250, relay 252 is energized in a circuit from battery through the Winding of said relay, contact 249 back contact and armature of relay 259, armature and contact of relay 2'79,,right hand arma-- ture and contact of relay 243, contact 274 5 to 1 to ground. The source of alternatinc; current 237 is disconnected at contacts "267 and 268 to permit the deenergization of Relay 873 opens the circuit or relay .373. relay 360 which in turn deenergizes and closes a circuit 'i'rom battery through the Winding of sequence switch 850, contact356 (2), back contact and armature relay 660 to ground. Sequence switch350 moves from position 2 into position 3. In position 3 of sequence'switch 850, relay 372 is energized by means of a circuit closed at con-,

tact 34:1 (3 to 8). Relay 372 attracts its armatures and completes a circuittrom. battery through the winding of relay 352, contact 344i (3 to 8) front contact and right hand armature of relay 372, conductor 361,

terminal 286, brush283, contact 268 (6 to 13), contact and armature oi": relay"272,.

Winding-of relay 279. contact 267 (6 to 13),

brush 282, terminal 285, conductor 802, lett; hand armature and front contact of relay 872,,contact 345 to8) to ground. Relay 279 energizes in this circuit and opens the holding circuit of relay 252. Relay 252 releases its armature and completes. a circuit including contact for driving .sequence' switch 250 ,out of position 6 and into position 7.

ct operate inseries'rvith rebranch exchange, however,

(1), right-hand 250, a circuit is momentarily closed from battery through the winding of relay 272, contact 256 (8 to 10), master contact 238 of sequence switch 250 to ground. Relay 272 remains energized until the sequenceswitch 250 reaches position 8. The energization of relay 27 2 opens the above-traced circuit for relays 352 and 279, permitting these relays to release their armatures. In position 8 of sequence switch 250 and after the release of the armature of relay 279, a circuit is closed from battery'through the winding of coil 236. right-hand winding of relay 259,

contact 266 (8). armature and contact of relay 279. right-hand armature and contact of relay 243, contact 274 (5 to 14) to ground. This circuit is closed slightly before the contact 258 closes in position 8. The differential relay 259, therefore operates and remains energized to prevent the disturbance of register 290 until relay 279 again energizes to open the circuit: through the righthand winding of relay 259.

Nhen relay 352 deenergizes in response to the energization of relay 272 in the central office, a circuit is completed from battery through the winding of sequence switch 350, contact 353 (3), back contact and armature of relay 352 to ground. Sequence switch 350 moves from position 3 into position 4. )Vith sequence switch 250 in position 8 and relay 27 2 deeuergized, the above-traced circuit is closed for the energization of relays 352 and 379. Relay 35 2 completes a circuit from ground through its armature and front contact, contact 347 (4), through the windin; of trip spindle power magnet 348, to battery and ground. The trip spindle power magnet energizes and causes the rota t-ion of the trip spindle in the well-known manner. When relay 279 energizes, with sequence switch 250 in position 8, the circuit through the right-hand winding of relay 259 is opened causing this relay to deenergize. As the brush-tripping spindle of the final connecting switch in. the private branch exchange approaches its first brush-tripping position, contacts 355 and 357 are closed to complete a circuit including contact349 (4 to 6). for shunting out relay 279. Relay 279 by retracting its armature completes a. circuit from battery through the winding of register 290, one of the two contacts 293 or 294 of register 290 dependent upon the position in which said register is standing, contact 258 (8), left-hand. winding and back contact and armature of relay 259, armature and contact of relay 279, right-hand; armature and contact of relay. 243, contact 274 (5 to 14), to ground. In parallel to this circuit, a circuit is also completed from battery through the winding of coil 236, righthand winding of relay 259, contact 266 (8), and thence to ground at contact 274. Thedifferential relay 259 remains inoperative whereas register 290 energizes and advances one position. In p-asslng between positions the master contact 291 short-circuits the left- 7 hand winding of relay 259 topermit said relay to energize. This operation continues until the register 290 has been restored to its normal position 0, at which time the trip spindle of the final switch will have advanced to a position for tripping the set of brushes having access to the desired group of subscribers lines. As soon, after the reg ister 290 reaches position 0, as relay 279 releases its armature, a circuit is established from battery through the winding of sequence switch 250, contact 292 (0) of regis ter 290, contact 258 (8), left-hand winding and back contact and armature of relay 259, armature and contact of relay 279, righthand armature and contact of relay 243, contact 274 (5 to 14), to ground. A parallel circuit is also completed Jirom battery through the winding of relay 272, contact 256 (8 to 10),and thence to ground at contact 274. Relay 272 operates to open the circuit of relay 352 and sequence switch 250 energizes and moves from position 8 into position 10. The next opening of contacts 355 and 357 after the energization of relay 272, causes the release of relay 352, which completes a circuit from ground through its armature and back contact. contact 353 (4), winding of sequence switch 350 to battery and ground. Sequence switch 350 advances from position 4 into position 6.

\Vhen sequence switch 250 leaves posltion 8, contact 258 is openedlto permit the deenergization of relay 27 2. The above traced circuit including relays 352 and 279 is then closed. Relay 352 attracts its armature and completes a circuit from battery through the winding of the brush carriage power magnet 361, contact 346 (,6), front contact and armature of relay 352 to ground. The magnet 361 causes the rotation of the brush carriage to advance the selected set of brushes 332, 333 and 334 into engagement with the terminals of the called line 300. For each'set of line terminals passed over by the brushes, a circuit is closed from battery through the winding of relay 352 contact-349 (4 to 6),

contact249-( to 13), bar contact and armature of relay 259, armature and contact of relay 279, right-hand armature and contact of relay 243, contact 274 (5 to 14), to ground. Thiscircuit maintains the energization of relay 252 but causes the shunting of the stepping relay 126 in the fundamental circuit. Relay 126 by retracting its armature closes a circuit for the advance of the units register 150 in the manner described in connection with the tens register 140.

This circuit nlay be traced '110111 battery through the winding of register 150, contact 152, contact 123 (12) of sequence swith 120, contact and armature and left-hand winding of relay 127, contact and armature of relay 126, to ground at contact 124. For each succeeding closure of the interrupter brush 306, relay 279 deenergizes to in turn cause the energization of the stepping relay 126 to cause the advance from position to position of the units register 150. )Vhen'register 150 reaches its 0 position, which determines that the brushes 332, and 334 have reached the terminals 335, 336 and 337 of the called line, a circuit is completed from battery through the winding of sequence switch 120, contact 121', contact 153 (0), contact 123 (12), contact and armature and left-hand winding of relay 127, contact and armature of relay 126, contact 124, to ground. The sequence switch 120 advances to its next position-while relay 125 is energized as above described to open the fundamental circuit. As soon, after theenergization of relay 125, as relay 279 becomes energized, relay 252 releases its armature and completes a circuit from battery through the winding of sequence switch 250, contact 254 (10), back contact and armature of relay 252 to ground. A circuit is also completed from battery through the winding of relay 272, contact 256 (8 to 10), contact 254 (10), back contact and armature of relay 252 to ground. Relay 272 opens the circuit or" relay 352 while sequence switch 250 energizes and moves into position 12. [is soon, after the energization of relay 272, as the interrupter brush 306 is opened. relay 352 deenergizes and completes a circuit from battery through the Winding of sequence switch 350, contact 353 (6 back contact and armature of relay to ground. Sequence switch 350 passes fr'oni'position 6 into 13051130118. With the sequence switch contact 256 open in position 12, relay 272 is permitted to deenergize and again complete a circuit for the energization of relays 352 and 279. d

'While' the sequence switch 350 is passing through. position 7, a test is made to deterinine the busy or idle condition ofa called line. Assuming the line to be idle, full potential is [found on terminal 337 and a circuit is closed'froin battery through the wind ing of relay 371', terminal 337, brush 334,

ground. This lowresistance path decreases the potential on terminal 337 to render the called line busy. In position 8 otsequence switch 350 a circuit. is completed from ground through the armature and back contact of relay 360, contact (S), winding of sequence switch 350 to battery and ground for driving sequence switch 350 into position 10. In leaving position .8, sequence switch 350 opens at its contact 341, the holding circuit of relay 372. This relay, however-,is energized in a circuit including contact 356 (9 to 10) and the back contact and armature of relay 360. In passing from position 8 to 10, sequence switch 350 opens its contacts 344 and 345 to cause the rnonientary deenergization of relays 352 and 279. Relay 279 by retracting its armature C0111: pletes a circuit from battery through the winding of relay 252, contact 249 (10 to .13), back contact and armature of relay 259, armature and contact of relay 279, righthand armature and contact of relay 243, contact 274 (5 to 14), to ground. Relay 252 becomes energized and completes a circuit from ground through its armature and front contact, contact 253 (12 to winding of sequence switch 250, to battery and ground. Sequence switch 250 leaves position 12. Be fore sequence switch 250 reaches position 13, however, relay 279 becomes energized in series with relay 352 and opens the circuit of relay 252. Relay252, therefore, deenergizes and sequence switch 250 stops at position 13.

With sequence switch 350 in. position 10 and relay 352 energized, a circuit is completed from ground through the armature and front contact of relay 352, contact 353 (10) winding of sequence switch 350 to battery and ground for moving said sequence switch into position 12. In position 12 ringing current is applied to the called line by means of a circuit traceable from the ringing source 320, contact 366 (12), brush 333, terminal 336, over the loop of the called line, and returning by way of terminal 335, brush 332, contact 367 (12), winding of relay 360 to battery and ground. When the'called subscriber responds by removing his receiver from the switc hhook, the marginal relay 360 ill) all)

gized in a circuit including sequence switch contact 3 11. When sequence switch 350 leaves position 12, 'contacts3414 and 3 15 are opened to cause the deenergization of relays 279 and 352. Relay 279 releases its armature and completes the above-traced circuit for relay 252. Relay 252 completes a circuit from ground through its armature and front contact, contact 253 winding of sequence switch 250 to battery and ground. Sequence switch 250 advances into position 14-. which is the talking position. lVith sequence switch contacts 216 and 2&7 closed in position 14, and sequence switch contacts 367 and 363 closed in position 14, a through circuit is established from the first group selector, shown in Fig. 1, to thecalled subscribers line. Talking battery is supplied in .the usual manner from the central ofiice and the supervisory relay 368 is energized n se I ries therewith. H

After the conversation has been .com pleted, the calling subscriber, by replacing his receiver on the switchhoolr, causesfthe release of the first group selector-switch in the well-known manner. The test brush 111 by disengaging test terminal 11 1, opens the holding circuit of relay 2&3. Relay2i3 releases its ar'rnatures and completes a circuit from battery through the winding of sequence switch 250,, make-before-break .contact of relay 243, contact 274: (5; to 14) to ground. Sequence switch 250 thereupon moves from positionli into position 17. In

position 17 of sequence switch 250, relay 252 becomes energized in a circuit from battery through the winding of said relay, contact 2 9 (17), baclr contact and armature of relay I 259, armature and contact of relay 279, con

tact 2'7e (15 to 18) to ground. The reason for energizing relay 252 is, as will be presently seen, to hold the sequence switch 250 from passing out of position 17 to render the outgoing end of the trunkidle until the switch at the distant end of the trunk has from position ld into position 15. Relay 360 releases its armature andconipletes a circuit including contact 356 (15), for driving sequence switch 350 out of 12031 21011 15 and intov position 16. In position 16, the

A circuit is then closed from commences to Sequence switch 350 advances above-traced circuit for relay360 is again closed through contact-37 6, and the contacts and armatures oi relays 3.68 and 352i Relay 360 becomes energized and completes a circuit including contact 354 (16) for moving sequence switch 350 into position 17. A. cir cuit is now'closed from battery through the winding of brush carriage power magnet, 361, contact 3 16 (:17), back contact and arnia ture of relay 352to ground'l Thebrush carriage con'iinences to rotate and on reaching 1 its normal p'osition, a circuit is completed from battery, through the winding of relay 352, contact 378 (17), contact 322, brush 323 to ground. Relay 352 opens the circuit of power magnet 361 anjd also completes a circuit from battery, through the winding of sequence switch 350, contact 353 (17), front contact and armature of relay 352 to ground.

Sequence switch 350 nioves into position 18.-

in position 18 of sequence switch 350, a circuit is established from battery, through the winding of relay 352, contact 3% (18) thence over the trunk conductor as hercinbefore traced, through the winding ofrelay 279, and returning to ground at contact 3415 (18). Relays 352 and 279 become energized. Relay 352 by attracting its armature, closes a circuit including, sequence switch contact 353 for driving, sequence switch 350 out of position 18. and into position 1. The relay 279 by attracting its armature, opens the circuitof relay 252. Relay v2'52 releases its armature and completes a circuit including contact 2541 (17) for moving sequence switch 250 into position 18. v

It will be observed that sequence switch 350v and sequence switch 250 are, advanced simultaneously from their respective positions, 18 and 17. Sequence sw1tch350, by

movin from position 18 into position 1,

opens the circuit of relay 372and closes the contact 3 11 to render the test terminal 3241 of the trunk line selectable by switches of the private branch exchange. T he sequence switch 250, in passing out of position 17' opens its contact 277 to render the test terminal 238 of the trunk lineselectable tov other switches in the central oflice. this arrangeme nt both ends of the two-way trunk are simultaneously released.

With sequence switch 250 in position 18a circuit is closed from battery through the winding of brush carriage power magnet 261, back contact and armature of relay; 262, contact 254 (13), back contactandarmature oi. relay/ 252 to ground. The brush carriage rotate andon reaching its nor mal position, tery through resistance, 24:2, contact .2411 (18), contact 2410 (18), contact 269, brush 235, winding of relav 262 to ground. Relay 262 becomes energized and opens the circuit of magnet 261 to stop the brush carriage. Relay 262 also establishes a circuit 'firornbata circuit is closed frornbat .ture

through position 7. Since relay 364 re tery through the winding of sequence switch 250, back contact and armature '01" relay 263, front contact and armature of relay 262, contact 254 (13), back contact and armature of relay 252 to ground. Sequence switch 250 thereupon advances into its normal posi-v tion 1. I I 7 It will now be assumed that the called line 300 is busy atthe time its terminals are tested by the final selector switch. This being the case, a reduced potential exists on test terminal 337 and relay 364 does not receive suflicient current to attract its arma-. when sequence switch 350 passes mains deenergized a circuit is closed from batterythrough the winding of relay 360, resistance 321, contact 376 (7 to 10), back contact and armature of relay 364 to ground.

Relay 360 attracts its armature and opens the circuit which would otherwise drive sequence switch 350 out of position 8.

Sequence switch 350, therefore, comes to rest in position 8 and contacts 344 and 345 remain closed to prevent the momentary deenergization of relay 279. The relay 252 the switchhook, causes the release of the,

' first group selector and the consequent de is therefore not energized in the manner above described and sequence switch 250 which has just advanced into position 12, remains in this position. A circuit is thereupon closed from ground through the in-- terrupter 278, contact 239 (12), prlmary winding of the tone coil 276, to battery and ground. The interrupter 278 causes the impression of a characteristic tone on the calling line which notifies the calling subscriber that the called line is busy. The calling subscriber, replacing his receiver on energization of relay 243. Relay 243 closes the circuit hereinbefore traced for advancing sequence switch 250 out of position 12 and intov position 17 Theopening of contacts 267 and 268 as sequence switch 250 leaves position 13, causes the deenergization of relay 352. Relay 352 completes a. circuit from ground through its armature and back contact, and contact 353(8) for driv-' lay.352, therefore, remains deenergized and a circuit is-completed from battery through the winding of brush carriage power mag- 11et 361, contact 346 (10), back contactand armature of relay 352 to ground. The brush carriage rotates and. onreaching' its closes acircuit including, contact 353 (10) for moving sequence switch 350 into position 12.v In position 12 ofsequence switch 350, relay 372 reinains-deenergized to pre-' vent the energization of relay 352 in series with relay 279. The relay 368 being deenergized, however, a circuit is closed as above described, for the energization of relay 360, including contact 376, contact and armature of relay 368 and the back contact and armature of relay 352. Relay 360 completesa circuit including contact 354 (12) for moving sequence switch 350 into posi tion 14. In position 14, relay 372 is again energized by means of a circuit closed at contact 341 (13 to 18). Contacts 344 and 345, being open inthis position however, relay 352 is still unable to energize in series with relay 279. Relay 360 is again energized in the circuit traced and closes the circuit including contact 354 (14), for driving sequenceswitch 350 into position 15. In position 15 relay 360 deenergizes and completes a circuit including contact 356 for driving sequence switch 350 into position .16. Relay 360 again energizes and prepares a circuit as explained for moving sequence switch 350 into position 17. In position 17 relay 352 isagain energized in a circuit over contact 378, contact 322, brush 323. Relay 352 completes a circuit including contact 353 (17), for moving sequence switch 350 into position 18. In position 18 of see quence switch 350., relay 352 becomes energized in series with relay 27 9 and from this point on the remainder of the disconnection takes place as hereinbefore described.

The private branch exchange disclosed in this system is assumed to have a capacity sufficiently large to utilize several levels of trunks in the switch at the central oflice. Aocordingly positions 4 and 9 of the individual register 290 are assigned to the establishment of connections to this particular pri-' vate branch exchange; The remaining positlons from 0 to 3 of register 290, in which positions contacts 220 and 221 are closed, may be assigned to the vestablishment. of connections to a smaller private branch ex. change requiring a comparatively few levels of trunks in the switch.

l/Vhat is claimed. is:

1. In a telephone exchange system, a tele- .3

phone line, a selective switch, a second selective switch, a plurality of switchcontrolling registers, means controlled in accordance. with the setting of one of said controlling registers for operating said first switch to extend the telephone line to said second switch, and means operated inaccordance with theextent of operation of said first switch for controlling the opera tion-of said second switch to further extend the telephone line. 1

2. In a telephoneexchange system, .a telephone line, a selective switch, a second selective switch, a plurality of switchcontrolling registers, means controlled in accordance with the setting of one of said registers for operating said first switch to extend the telephone line to said second switch, means operated in accordance with the extent of operation of said first switch for COIltIolling the selective operation of said second switch, and means controlled in accordance with the setting of another of said controlling registers for further selectively operating said second switch to extend the telephone line.

3. In a telephone exchange system, a telephone line, a selective switch, a second selective switch, a plurality of switchcontrolling registers, means controlled in accordance with the setting of one of said registers for operating said first switch to extend the telephone line to said second switch, an additional register, means for setting said additional register in accordance with the extent of operation of said first switch. and means controlled in accordance with the setting of said additional re ister for selectively operating said second switch to further extend the telephone line.

4. In a telephone exchange system, a telephone line, a selective switch, a second selective switch, a plurality of switchcontrolling registers, means controlled in accordance with the setting of one of said registers for operating said first switch to extend the telephone line to said second switch, an additional register individual to said first switch, means for setting said additional register in accordance with the extent of operation of said first switch, and means controlled in accordance with the setting of said additional register for selectively operating said second switch to further extend the telephone line.

5. In a telephone exchange system, a telephone line, a selective switch, a second selective switch, a plurality of switchcontrolling registers, means controlled in accordance with the setting of one of said registers for operating said first switch to extend the telephone line to said second switch, an additional register individual to said first switch, means for setting said additional register in accordance with the extent of operation of said first switch, and means controlled in accordance with the setting of said additional register for selectively operating said second switch, said last means being also controlled in accordance with the setting of another of said controlling registers for further selectively operating said second switch toextendthe telephone line. v i

6. Inla telephone exchange system, a tele phone line, a selective switch having brushes 'and'a brush-selecting element, a

' the telephone line.

, second selective switch," a plurality of 7. In a telephone exchange system, a tele- I phone line, a selective switch having brushes and a brush-selecting element, a second selective switch, a plurality of switch-controlling registers, means controlled in accordance with the setting of one of said registers for operating said brushselecting element to select a set of brushes,

means for operating the selected brushes I of said first switch to extend the telephone line to said second switch, means for restoring said brush-selecting element to its normal position, and means operated in response to the restoration of said brush-. selecting element for controlling the selective operation of said second switch 'to further extend the telephone line.

8. In a telephone exchange system, a selective switch, a trunk line, a second selective switch, means for operating said first switch to extend a connection over said trunk to said second switch, means for operating said second switch to further extend said connection, means for rendering said trunk busy at said first switch, means for rendering said trunk busy at said second switch, means for releasing said switches, and means operated during the release of said switches for removing the busy condition of said trunk at both switches simultaneously.

9. In a telephone exchange system, a telephone line, a selective switch having brushes and a brush selecting device, a second selective switch, means for operating said brush selecting device to select a set of brushes, means for operating the selected brushes of the first switch to extend the telephone line to said second switch, and means operated in accordance with the extent of operation of said brush selecting device for controlling the selective operation of said second switch to further extend the telephone line.

10. In a telephone exchange system, a

telephone line, a selective switch having brushes and a brush selecting. device, a second selective switch, means for, operating operated in response to the restoration of said brush selecting device to select aset of said brush selecting device; for controlling brushesof said first switch, means for operthe selectiveoperation of said second switch 10 ating the selected set of brushesto extend to further extend the telephone line.

the telephone line to said second switch, In 'Wl-tIlBSS, whereof, I hereunto subscribe means for restoring-the brush selective de my namethis 2nd day of April A .D., 1820.

vice to itsvnormal condition, and means LIPAiPoLINKoWsKY 

